Nonlinear control of center-node UPFC and VSC-based FACTS controllers.

摘要

Voltage-Source Converters form the basic modules of a class of power electronic controllers of Flexible AC Transmission Systems (FACTS) which include the STATic COMpensator (STATCOM), the Static Synchronous Series Compensator (SSSC) and the Unified Power Flow Controller (UPFC). The mathematical equations which model a Voltage-Source Converter (VSC) are nonlinear (bilinear) because the system inputs are multiplied by a state-variable. The high performance characteristics for their operation must be designed in the face of the nonlinearity. This thesis applies a Nonlinear Control Method which makes use of a nonlinear transformation to obtain a system of linear equations. Then linear state feedback is used to move the eigenvalues of the linear system to achieve fast, stable response.; The Nonlinear Control Method has been applied successfully to 3 FACTS controllers: (1) the single VSC SSSC (system order N = 3); (2) the 2-VSC UPFC (N = 5); and (3) the 3-VSC Center-node Unified Power Flow Controller (C-UPFC, N = 5). The key to success is in finding the nonlinear transformation equations which is an art as in all integration efforts and which cannot be taught as in differentiation. Having found the nonlinear transformation equations for the 3 FACTS controllers, they can be extended to the entire family of Voltage-Source Converter based FACTS controllers.; A Simplified Nonlinear Control Method, which does not sacrifice mathematical rigour, is proposed. As the Simplified Nonlinear Control Method does not require knowledge in advanced control theory, it facilitates adoption of the Nonlinear Control Method by the power electronics community.; The thesis also covers in-depth research on the Center-node Unified Power Flow Controller (C-UPFC), an innovative FACTS controller. The research shows that it has all the capabilities of Lazslo Gyugyi's Unified Power Flow Controller. In addition, as a controller conceived to operate at the mid-point of a radial transmission line, it can double the power transmissibility of the line.